An attempt at modelling the diets of two sympatric species of hake (Merluccius capensis and Merluccius paradoxus) off the coast of Namibia: isotope mixing model approach

Abstract

Two species of hake, Merluccius capensis and Merluccius paradoxus, are the most important secondary consumers in the Benguela current ecosystem. To better understand hake diets in the northern Benguela (Namibia), the stable carbon (13C) and nitrogen (15N) isotope ratios of their muscles, and that of their prey (Hake, n = 115 and prey, n=299) were analysed. Results indicated that their diets were dominated by Plesionika martia, Chlorophthamus agazizi, Myctophids and Euphausiids. The highest contributor to the diet of M. paradoxus varied with length, while the diet of M. capensis was dominated by myctophids at all length classes. Cannibalism accounted for less than 6% and less than 4% in the diets of M. capensis and M. paradoxus respectively. Isotope based estimates of prey dietary contributions differed from that of previous gut content analyses. Overall, the results support the hypothesis that the two species have similar diets. Application of a Bayesian mixing isotope model can be improved to allow for improved hake consumption (i.e. annual) estimates to be made.